Wireless exploration seismic system

ABSTRACT

Systems and methods for seismic data acquisition employing a dynamic multiplexing technique. The dynamic multiplexing technique may include advancing one or more modules in a seismic array through a multiplexing signature sequence in successive transmission periods. The multiplexing signature sequence may be random or pseudo-random. A shared multiplexing signature sequence may be used at all the modules in the seismic array. As such, modules belonging to a common collision domain may operate out of phase with respect to the shared multiplexing signature sequence.

This application is a continuation of U.S. patent application Ser. No.12/982,416 entitled “WIRELESS EXPLORATION SEISMIC SYSTEM” filed on Dec.30, 2010 which claims priority as a continuation-in-part to U.S. patentapplication Ser. No. 12/837,177 filed on Jul. 15, 2010 entitled“WIRELESS EXPLORATION SEISMIC SYSTEM,” which is a continuation of U.S.patent application Ser. No. 11/538,744 filed on Oct. 4, 2006 entitled“WIRELESS EXPLORATION SEISMIC SYSTEM” now U.S. Pat. No. 7,773,457 whichclaims priority to U.S. Provisional Application No. 60/724,271 filed onOct. 7, 2005 and U.S. Provisional Application No. 60/821,217 filed onAug. 2, 2006. The entire disclosures of the foregoing being are herebyincorporated by reference in their entirety as if set forth in fullherein.

FIELD

The present disclosure relates to systems and methods seismic surveysystems where the data signals from multiple sensors are transmitted bywireless means. In particular, the present disclosure relates to systemsand methods that facilitate real time read out of a seismic surveysystem, even in the case of rapidly repeating vibrating energy sources,without backlogging of data or delay of the survey process.

BACKGROUND

Seismic surveys are often used by natural resource exploration companiesand other entities to create images of subsurface geologic structure.These images are used to determine the optimum places to drill for oiland gas and to plan and monitor enhanced resource recovery programsamong other applications. Seismic surveys may also be used in a varietyof contexts outside of oil exploration such as, for example, locatingsubterranean water and planning road construction.

A seismic survey is normally conducted by placing an array of vibrationsensors (accelerometers or velocity sensors called “geophones”) on theground, typically in a line or in a grid of rectangular or othergeometry. Vibrations are created either by explosives or a mechanicaldevice such as a vibrating energy source or a weight drop. Multipleenergy sources may be used for some surveys. The vibrations from theenergy source propagate through the earth, taking various paths,refracting and reflecting from discontinuities in the subsurface, andare detected by the array of vibration sensors. Signals from the sensorsare amplified and digitized, either by separate electronics orinternally in the case of “digital” sensors. The survey might also beperformed passively by recording natural vibrations in the earth.

The digital data from a multiplicity of sensors is eventually recordedon storage media, for example magnetic tape, or magnetic or opticaldisks, or other memory device, along with related information pertainingto the survey and the energy source. The energy source and/or the activesensors are relocated and the process continued until a multiplicity ofseismic records is obtained to comprise a seismic survey. Data from thesurvey are processed on computers to create the desired informationabout subsurface geologic structure.

In general, as more sensors are used, placed closer together, and/orcover a wider area, the quality of the resulting image will improve. Ithas become common to use thousands of sensors in a seismic surveystretching over an area measured in square kilometers. Hundreds ofkilometers of cables may be laid on the ground and used to connect thesesensors. Large numbers of workers, motor vehicles, and helicopters aretypically used to deploy and retrieve these cables. Explorationcompanies would generally prefer to conduct surveys with more sensorslocated closer together. However, additional sensors require even morecables and further raise the cost of the survey. Economic tradeoffsbetween the cost of the survey and the number of sensors generallydemand compromises in the quality of the survey.

In addition to the logistic costs, cables create reliability problems.Besides normal wear-and-tear from handling, they are often damaged byanimals, vehicles, lightning strikes, and other problems. Considerablefield time is expended troubleshooting cable problems. The extralogistics effort also adds to the environmental impact of the survey,which, among other things, adds to the cost of a survey or eliminatessurveys in some environmentally sensitive areas.

As a result, wireless acquisition units have been developed to do awaywith the burdensome nature of cables in such a system. For instance,U.S. Pat. No. 7,773,457, which is hereby incorporated in its entirety byreference as if reproduced herein, describes a system for performing aseismic survey using wireless acquisition units.

When conducting a survey using wireless data acquisition units, it maybe advantageous to perform a wireless data read out from such units inreal time. As such, survey verification may occur prior to theconclusion of the survey, and the cost and time associated with manualdata retrieval of such units may be reduced or eliminated. However, whenemploying a real time data read out, the bandwidth usage of the wirelesscommunication between modules must be carefully considered so as not toslow the speed at which the survey is conducted.

In turn, a multiplexing regime may be imparted to the wireless modulesin the seismic survey so that multiple units within range of one anothermay simultaneously broadcast and receive data. Examples of suchmultiplexing regimes include time division, frequency division, codedivision, etc. For example, U.S. Pat. No. 7,773,457 describes employingmultiplexing techniques in a “bucket brigade” type system to performreal time read out of data.

SUMMARY

It has been recognized that a dynamic multiplexing technique, whereinthe multiplexing signature used to multiplex a signal is varied atdifferent time periods, may be provided for use in systems such as thosedescribed in U.S. Pat. No. 7,775,457. For example, when using frequencydivision multiplexing, regulatory bodies such as the FederalCommunication Commission in the United States may enforce regulationsrequiring that no single frequency may be used by a module for longerthan a set duration. As such, a dynamic multiplexing technique may allowfor operation in such cases where static multiplexing is not feasible.

When employing such a dynamic multiplexing technique, a random orpseudo-random multiplexing regime may be employed wherein each unit usesa different random multiplexing signature during successive transmissionperiods. However, with multiple units using a random or pseudo-randommultiplexing signature, two units may simultaneously attempt to use thesame multiplexing signature to transmit data. In such instances, a datacollision may occur and the units may each be required to retransmit thedata which was subject to the collision. These retransmissions mayreduce the bandwidth of the system, which may slow the survey. This mayadd additional time and cost to the survey, and is thus preferablyavoided. For example, in the case of two units operating within a commoncollision domain, it has been found that the bandwidth of the system maydecrease by between 3%-5%. This may add additional time and cost to thesurvey, and is thus preferably avoided. As the number of units within acollision domain increases, the problem is exacerbated and the bandwidthcan deteriorate much more than the amount listed above.

Accordingly, a first aspect includes a method for use in seismic dataacquisition. The method includes disposing, in series, a plurality ofseismic data acquisition modules that are operative to wirelesslycommunicate acquired seismic data. The acquisition modules define awireless serial data transfer path for relaying data from upstreamacquisition modules to downstream acquisition modules and a datacollection unit. The method further includes assigning a firstacquisition module in said serial data transfer path a firstmultiplexing signature sequence. In successive transmission periods, thefirst acquisition module advances sequentially through a first pluralityof multiplexing signatures of the first multiplexing sequence. Themethod further includes assigning a second acquisition module in saidserial data transfer path a second multiplexing signature sequence. Insuccessive transmission periods, the second acquisition module advancessequentially through a second plurality of multiplexing signatures ofthe second multiplexing sequence.

A number of feature refinements and additional features are applicableto the first aspect. These feature refinements and additional featuresmay be used individually or in any combination. As such, each of thefollowing features that will be discussed may be, but are not requiredto be, used with any other feature or combination of features of thefirst aspect.

For example, in one embodiment, the method may further include firsttransmitting, using a first multiplexing signature of the firstplurality of multiplexing signatures, seismic data from the firstacquisition module to at least one downstream acquisition module andsecond transmitting, using a second multiplexing signature from thesecond plurality of multiplexing signatures, seismic data from thesecond acquisition module to at least one downstream acquisition module.

In an embodiment, the first multiplexing signature sequence and thesecond multiplexing signature sequence may be a random sequence ofmultiplexing signatures. In turn, the method may further includedetecting when the first multiplexing signature used in the firsttransmitting is the same as the second multiplexing signature used inthe second transmitting. The method may also include firstretransmitting, using the next multiplexing signature from the firstmultiplexing signature sequence, seismic data from the first acquisitionmodule to at least one downstream acquisition module and secondretransmitting, using the next multiplexing signature from the secondmultiplexing sequence, seismic data from the second acquisition moduleto at least one downstream acquisition module.

In one embodiment, the first multiplexing signature may be differentthan the second multiplexing signature. Additionally, at least a portionof the first transmitting and at least a portion of the secondtransmitting may occur during a common transmission period. In anembodiment, the first multiplexing signature sequence and the secondmultiplexing signature sequence may be the same pseudo-random sequenceof multiplexing signatures. Furthermore, the first acquisition moduleand the second acquisition module may operate out of phase with respectto the shared pseudo-random sequence of multiplexing signatures. In oneembodiment, the multiplexing signatures comprise a plurality ofdifferent frequencies.

In yet another embodiment, the method includes assigning the firstmultiplexing signature sequence to a third data acquisition module. Thefirst and third acquisition modules may be positioned in the serialtransmission path at first and second locations. A distance between thefirst and second locations may be greater than a transmission range ofthe first and third acquisition modules.

A second aspect includes a method for use in seismic data acquisition.The method includes disposing a plurality of seismic data acquisitionmodules in an array. Each seismic data acquisition module is operativeto wirelessly communicate with at least one other seismic dataacquisition module in said array to define at least a first serial datatransmission path. Additionally, the method includes assigning each ofsaid plurality of seismic data acquisition modules in said first serialdata transmission path a multiplexing signature sequence for use intransmitting said seismic data. At least one multiplexing signature isassigned to first and second seismic data acquisition modules in saidfirst serial data transmission path during a first common transmissionperiod. The method also includes, during the first common transmissionperiod, transmitting seismic data from said first and second seismicdata acquisition units using said at least one multiplexing signature.Also, the method includes advancing the first and second seismic dataacquisition modules in the multiplexing signature sequence such that thefirst and second seismic data acquisition modules are assigned at leastone different multiplexing signature during a second common transmissionperiod.

A number of feature refinements and additional features are applicableto the second aspect. These feature refinements and additional featuresmay be used individually or in any combination. As such, each of thefollowing features that will be discussed may be, but are not requiredto be, used with any other feature or combination of features of thesecond aspect.

For instance, in one embodiment the multiplexing signature sequence maybe a random sequence of multiplexing signatures. Additionally, themethod may also include detecting a data collision between the first andsecond seismic data acquisition unit during the first commontransmission period and retransmitting the seismic data during thesecond common transmission period using the at least one differentmultiplexing signature.

In an additional embodiment, the multiplexing signature sequence may bea pseudo-random sequence. The multiplexing signature sequence for thefirst seismic data module and the second seismic data module may be thesame. As such, the first seismic data module and the second seismic datamodule may be out of phase with respect to the multiplexing signaturesequence.

A third aspect includes a system for use in seismic data acquisition.The system includes a plurality of seismic data acquisition modules,disposed in series, that are operable to wirelessly communicate acquiredseismic data. The acquisition modules define a wireless serial datatransfer path for relaying data from upstream acquisition modules todownstream acquisition modules and a data collection unit. The systemfurther includes a first acquisition module in said serial data transferpath for transmitting seismic data using a first multiplexing signaturefrom a first multiplexing signature sequence during a first transmissionperiod. The first acquisition module advances through the firstmultiplexing signature sequence in successive transmission periods.Additionally, the system includes a second acquisition module in theserial data transfer path for transmitting seismic data using a secondmultiplexing signature from a second multiplexing signature sequenceduring the first transmission period. The second acquisition moduleadvances through said second multiplexing signature sequence insuccessive transmission periods. The first multiplexing signature andsaid second multiplexing signature are different during the firsttransmission period.

A number of feature refinements and additional features are applicableto the third aspect. These feature refinements and additional featuresmay be used individually or in any combination. As such, each of thefollowing features that will be discussed may be, but are not requiredto be, used with any other feature or combination of features of thethird aspect.

In one embodiment, the first multiplexing signature sequence and saidsecond multiplexing signature sequence may be a common pseudo-randomsequence of a plurality of frequencies. The first acquisition module andsaid second acquisition module may be out of phase with respect to thecommon pseudo-random sequence.

In another embodiment, the system may include a third acquisition modulein said serial data transfer path for transmitting seismic data usingthe first multiplexing signature from the first multiplexing signaturesequence during the first transmission period. The third acquisitionmodule may advance through said first multiplexing signature sequence insuccessive transmission periods. Additionally, the first acquisitionmodule and third acquisition module may be at a first location and asecond location. The first location and second location may be separatedby a distance greater than the transmission range of the first and thirdacquisition module. In this regard, the first and third module may be inphase with respect to the common pseudo-random sequence.

Furthermore, a number of feature refinements and additional features areapplicable to any of the foregoing aspects. These feature refinementsand additional features may be used individually or in any combination.As such, each of the following features may be, but are not required tobe, used with any other feature or combination of features of theforegoing aspects.

For example, the multiplexing sequence for the one or more modulesdescribed above may reside in non-volatile storage at each unit. Thatis, the multiplexing sequence may be stored locally in a memory of themodule. Alternatively or additionally, the multiplexing sequence may betransmitted among units (e.g., from a base unit to individual unitsdisposed in the array). In this regard, the multiplexing sequence may beupdated or modified during a survey. The transmitted sequence may inturn be stored in memory once received at the module.

In addition, the modules may comprise a seismic array. The seismic arraymay be of any appropriate configuration. For example, the modules of anyof the foregoing aspects may be arranged in lines to communicate to abase station. The modules may transmit to an adjacent module in the lineor the modules may transmit to a non-adjacent module. As such, eachmodule may communicate sequentially down the line to the base station oreach module may jump adjacent modules and transmit to non-adjacentdownstream modules.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an embodiment of a seismic survey area.

FIGS. 2A and 2B are schematic view of a first and a second wirelessacquisition unit pair employing frequency division multiplexing totransmit seismic data.

FIGS. 3-6 are charts graphically depicting the respective relativeportion of a first and second acquisition unit pair at differenttransmission periods.

FIG. 7 is a flow chart depicting an embodiment of a process for avoidingdata collisions.

FIG. 8 is a flow chart depicting another embodiment of a process foravoiding data collisions.

FIG. 9 is a schematic view of another embodiment of a wireless array.

FIG. 10 is a schematic view of a portion of an embodiment of a wirelessarray shown in three different instances of operation.

FIG. 11 is a schematic view of yet another embodiment of a wirelessarray.

FIG. 12 is a schematic view of a wireless array shown at variousinstances of operation.

FIG. 13 is a schematic view of still another embodiment of a wirelessarray.

DETAILED DESCRIPTION

While the invention is susceptible to various modifications andalternative forms, specific embodiments thereof have been shown by wayof example in the drawings and are herein described in detail. It shouldbe understood, however, that it is not intended to limit the inventionto the particular form disclosed, but rather, the invention is to coverall modifications, equivalents, and alternatives falling within thescope of the invention as defined by the claims.

FIG. 1 shows one possible configuration of a seismic data acquisitionsystem 100 in accordance with an embodiment of the present invention.The seismic acquisition system 100 may include all or any of thefeatures described in U.S. Pat. No. 7,773,457. For example, a number ofremote modules 101 may be arranged in lines as is done with previouswired systems, except that there is no physical connection between theremote modules 101. Base station modules 102 are provided which may beconnected to a central control and recording system 103 by Ethernet,fiber optic, or other digital data link or a wireless substitute.Example radio links operating on frequencies F1 to F12 are indicated byarrows. Note that for improved data rate, each radio link in theillustrated embodiment leaps past the nearest remote module to the nextmodule closer to the base station. Other radio transmission paths arepossible, including direct to the nearest remote module, leapingmultiple modules, or in the case of an obstruction or equipment fault,past a defective remote module or even across to another line or anyother logical path that establishes a communication flow. The centralcontrol and recording system 103 may be a notebook computer or largerequivalent system. In the various implementations of a wirelessacquisition system described above, each of the wireless modules beingcontrolled by a single base station may be referred to as a linesegment. This line segment may be further divided into one or moresubnets. Each subnet may comprise an independent serial data transferpath in a line segment. In this regard, and as shown in FIG. 1, a basestation unit 102 may be disposed such that a portion of the line segmentare arranged on opposite sides of the base station. That is, the basestation may reside at a point within the line segment. The portions oneither side of the base station of the line segment may be symmetric ormay not be symmetric. The portions of the line segment on either side ofthe base station may each comprise a subnet such that each moduletransmits to an adjacent module rather than the embodiment depicted inFIG. 1 wherein each module transmits to a non-adjacent module nearer thebase station. Furthermore, each portion of the line segment on eitherside of the base station may comprise multiple subnets as shown whereinmodules transmit to non-adjacent modules. In this regard, modules may beinterleaved such that there is more than one subset in a line segment.

For example, with additional reference to FIG. 9, each module 101 maycommunicate with an adjacent module such that no modules are skipped.FIG. 10 shows a similar configuration as shown in FIG. 9, wherein eachmodule 101 transmits to an adjacent module. FIG. 10 shows a portion of aline segment in various instances in time (T1, T2, and T3). At eachsuccessive time interval, different modules may transmit data (e.g.,appending acquired seismic data to the transmission) such that the datais in turn passed down the line segment to a base station 102. A fullarray of this sort is shown in FIG. 11. Note that either side of a linesegment may each comprise a subnet of modules. The base stations 102 mayreceive a transmission from a respective one of the different subnets indifferent transmission cycles. In this regard, and as illustrated inFIG. 12, a number of subnets may be provided that may transmit data backto a base station 102. The number of subnets may correspond on thenumber of cycles required for each subnet to subsequently transmit datato the base station 102. Alternatively, as shown in FIG. 13, basestations 102 may be provided with multiple radios to receivetransmissions from more than one subnet at the same time. In thisregard, for an embodiment wherein the base station unit interrupts theline segment and is positioned therein, the base station unit may havemultiple radios operative to receive the data multiple subnets at thesame time. Alternatively, the subnets may transmit to the base stationin alternating time periods such that each subnet transmits data to thebase station at different periods as shown in FIGS. 10-12.

In this regard, any given one of the remote modules 101 may bepositioned within transmission range of one or more other remotemodules. Accordingly, collision domains (e.g., areas having thepotential for interference or crosstalk between modules) are introducedinto the system. Each module may have a unique collision domain whereinpotential interference with other modules may occur. One or moremultiplexing techniques may be used to reduce the potential forcollisions of transmitted seismic data in the data acquisition system.For instance, each of the remote modules 101 transmitting data may do soon one of a plurality of different frequency ranging from F1 to F12 asrepresented in FIG. 1. In this regard, even if all the transmissionsoccur during a common transmission period, use of the differentfrequencies allow for the simultaneous transfer of seismic data withreduced potential for data collisions. Accordingly, modules receivingdata may only listen for the particular frequency such that otherseismic data transferred at a different frequency is not received.

Other multiplexing techniques may also be used. For example, each of theremote modules 101 may use a different code in a code divisionmultiplexing technique. Further still, each module 101 may transmit in adifferent discrete time period in a time division multiplexingtechnique.

In this regard, different multiplexing regimes may be applied to awireless acquisition unit system such as the one shown in FIG. 1. Asused herein, a multiplexing regime refers to the type of multiplexingused. As such, a multiplexing regime may be, but is not limited to,frequency division multiplexing, code division multiplexing, timedivision multiplexing or other appropriate multiplexing techniques. Amultiplexing regime may employ a plurality of unique multiplexingsignatures. The multiplexing signature is a unique parameter assigned toeach of the remote modules. As such, in the example provided in FIG. 1,the plurality of frequencies F1-F12 each represent a unique multiplexingsignature. Other multiplexing signatures may also be provided, such asdifferent codes for use in code division multiplexing or differentdiscrete time periods for use in time division multiplexing.

In addition to the static multiplexing technique depicted in FIG. 1wherein each module in a collision domain employs a static multiplexingsignature for transmission of data, a dynamic multiplexing regime may beemployed in such a system 100. This may allow for use of the system injurisdictions where regulatory bodies prevent the use of a singleconstant frequency by any particular device for longer than a setduration. As such, these units may frequency hop (i.e., changefrequencies) after the unit operates at a particular frequency for apredefined duration. As such, these units may include a random orpseudo-random sequence of multiplexing signatures. The unit may randomlyhop frequencies in successive transmission periods such that no singlefrequency is used longer than the predefined duration. This type ofrandom frequency hopping may be employed by each of the modules in asystem.

For instance, the system shown in FIG. 1 may employ such a randomfrequency hopping technique. As such, each of the frequencies shownF1-F12 may actually be a random or pseudo-randomly generated frequency.These random or pseudo-random frequencies may be bounded at upper andlower ends and may include a number of discrete frequencies that aredefined within a range of operating frequencies. In successivetransmission periods, each remote module 101 may randomly hop to anotherrandom frequency.

One such embodiment of a frequency hopping technique may be FrequencyHopping Spread Spectrum (FHSS). In an FHSS system, the initiating partysends a request via a predefined frequency or control channel to thereceiving party. The receiving party may return an index number to theinitiating party. The initiating party may uses the index number todetermine one or more frequencies (e.g., a pseudo-random sequence offrequencies to use). In turn, the initiating party may send asynchronization signal on the first frequency in a predeterminedsequence. This synchronization signal may synchronize the transmissionperiods of the module and serve as an acknowledgement to the receivingparty that the initiating party has correctly determined the frequencysequence. In turn, data may be transmitted with both the initiating andreceiving party hopping frequencies in the predefined sequence insuccessive transmission periods.

However, this random frequency hopping introduces a collision domaininto the system because two modules may randomly employ the samemultiplexing signature such that a data collision occurs. It has beenestimated that the occurrence of two modules hopping to the same randomfrequency may reduce the bandwidth of a system by 3% to 5%. This isbecause once a data collision occurs, each module may hop to anotherrandom multiplexing signature in the multiplexing regime and retransmitthe data, effectively losing one duty cycle for each of the collidingmodules.

Accordingly, another embodiment of a dynamic multiplexing regime mayinclude assigning a shared pseudo-random multiplexing signature sequenceto each of the modules in a system. In this regard, each module in thesystem may be assigned an identical multiplexing signature sequence.This shared pseudo-random multiplexing signature sequence may include asequence of frequencies, codes, or other different multiplexingsignatures. By using an identical multiplexing signature sequence, thepotential for two modules randomly hopping to the same multiplexingsignature may be reduced by controlling the phase of each module withrespect to the multiplexing signature sequence. Stated differently, themodules within a collision domain may operate out of phase from eachother with respect to the multiplexing signature sequence. As each ofthe modules may advance through the shared multiplexing signaturesequence at the same rate (e.g., one multiplexing signature pertransmission cycle), once modules within a given collision domain becomeout of phase from one another, the occurrence of data collisions may beminimized while still achieving a dynamic multiplexing environment.

This concept is further demonstrated with reference to FIG. 2A, whichdepicts a first seismic acquisition unit pair 200 and a second seismicacquisition unit pair 300. The first seismic acquisition unit pair 200shares a collision domain with the second seismic acquisition unit pair300 such that without a multiplexing technique, transmission between thefirst seismic acquisition unit pair 200 and the second seismicacquisition unit pair 300 may result in a data collision or crosstalkbetween the pairs. In this regard, the first seismic acquisition unitpair 200 may be within transmission range of the second seismic dataacquisition unit pair 300. However, as shown in FIG. 2A, a first seismicacquisition unit 210 transmits to a second seismic acquisition unit 220using a first frequency F1. At the same time, a third seismicacquisition unit 310 may transmit to a fourth seismic acquisition unit320 using a second frequency F2. As such, crosstalk and/or datacollisions are avoided and each seismic acquisition unit pair transmitsdata without interference using a unique multiplexing signature.

FIG. 2B depicts the same first seismic acquisition unit pair 200 andsecond seismic acquisition unit pair 300 shown in FIG. 2A. However, asshown in FIG. 2B, the transmission between the first seismic acquisitionunit 210 and the second seismic acquisition unit 220 as well as thetransmission between the third seismic acquisition unit 310 and thefourth seismic acquisition unit 320 uses a common frequency F3. Theresult would be a data collision such that the data transmitted betweeneach of the unit pairs 200 and 300 may be subject to a collision. Inturn, neither the second seismic acquisition unit 220 nor the fourthseismic acquisition unit 320 may accurately receive the data intendedfor the respective modules. This is an example of a situation where inprior systems, each unit pair would in turn randomly hop within a randomsequence and retransmit the data attempted to be transmitted in FIG. 2B.

Such an instance is also depicted in FIG. 3. FIG. 3 includes a chart 400depicting the frequency at which the first unit pair 100 and a secondunit pair 200 are operating. A sequence of pseudo-random frequencies 410are represented in the middle column of the table 400 and includefrequencies f₀ through f_(n). Any number of unique multiplexingsignatures may be used. In addition, while f₀-f_(n) are numberedconsecutively, the pseudo-random frequencies may not be consecutivelyarranged and may jump to different (i.e., higher and lower frequencies)in the spectrum without limitation. That is, the order of f₀-f_(n) doesnot necessarily indicate an increase or decrease in frequencies, butrather each subsequent frequency or multiplexing signature in thesequence may be random. As shown, both the first unit pair 100 and thesecond unit pair 200 are operating using a common frequency f₀. Thiscorresponds to the situation shown in FIG. 2B where a collision mayoccur.

In one particular embodiment, a total of sixty-four differentmultiplexing signatures may be employed in order to transmit databetween modules. For example, these sixty-four multiplexing signaturesmay comprise different frequency signatures residing in the 2.4 GHzband. Additionally, fifteen multiplexing signatures may be used that arededicated to deployment, formation, and wake-up system functions. Inthis regard, these fifteen multiplexing signatures may be used in aconfiguration mode in order to order and establish the array.

In accordance with the present invention, rather than having each of thefirst unit pair 100 and second unit pair 200 randomly sequence among thepseudo-random frequency signature sequence upon occurrence of acollision, the second unit pair 200 is advanced out of turn in thefrequency sequence 410. The first unit pair 100 may maintain itsposition in the frequency sequence 400 while the second unit pair 300 isadvanced. As such, the modules may operate as depicted in FIG. 4,wherein the first unit pair 200 operates at f_(o) while the second unitpair 300 operates at f₁. Alternatively, the first unit pair 200 may beadvanced by a single step in the sequence and the second unit pair 300may be advanced further out of turn (e.g., by two frequencies). As such,a retransmission of data may occur such that no data collision occurs.Additionally, the first unit pair 200 is now out of phase from thesecond unit pair 300 with respect to the frequency sequence 410.

Furthermore, upon successive transmission periods, such as the one shownin FIG. 5, the first unit pair 200 and second unit pair 300 may advanceat the same rate through the frequency sequence so as to stay out ofphase with respect to the common frequency sequence 410 shared betweenthe first unit pair 200 and the second unit pair 300. This may continueuntil the time period shown in FIG. 6 wherein the first unit pair 200remains on the last frequency f_(n) in the frequency sequence 410 whilethe second unit pair 300 recommences from the beginning of the frequencysequence 410. In turn, once one of the unit pairs is advanced out ofsequence different than the other unit pair, the unit pair will remainon different multiplexing signatures in the pseudorandom sequence andthus avoid data collisions.

In this regard, rather than the ongoing potential of data collisionswhen using a purely random multiplexing signature hopping technique, theforegoing allows the wireless acquisition units to hop to differentmultiplexing signatures without the potential for data collisions solong as the units in a given collision domain remain out of phase fromone another. The manner in which unit pairs are set to be out of phasefrom one another may vary in different embodiments. For instance, thecollision domain for each individual module may be manually analyzed andrespective collision domains may be determined for each acquisitionunit. In turn, acquisition units identified as belonging to a commoncollision domain may be set such that each unit in the collision domaininitiates operation out of phase with respect to each other unit in thecollision domain. Based on this information, the modules are manuallyset to be out of phase from one another. This manual setting of themodules out of phase from one another may occur at the deployment or setup of the modules.

Alternatively, a collision detection method may be employed such thatthe modules begin communicating according to the sequence. Only when acollision is detected do the two colliding modules act in accordancewith the foregoing such that one of the modules is advanced out of phasefrom the other. This out of phase advancement of one module may resultin the module advancing a single point or may randomly advance throughthe sequence to a different point than the other colliding module. Assuch, a learning protocol may be employed such that the modules in thecollision domain identify a collision and learn to settle into themultiplexing signature sequence such that each module in the collisiondomain is out of phase.

One example of a process 700 for performing such a dynamic multiplexingtechnique is shown in FIG. 7. The process 700 may include assigning 710a multiplexing signature sequence to a first and a second module. Theprocess 700 may further include transmitting 720 seismic data from thefirst and the second module using at least one multiplexing signature ateach one of the first and second module. In this regard, the first andsecond module may operate using a common multiplexing signature. In thisregard, a collision may be detected 730. Upon detection 730 of acollision, the process 700 may include offsetting 740 one of the firstor second modules such that the first and second module are out of phasefrom each other with respect to the multiplexing signature sequence asdiscussed above with regard to FIGS. 4-6.

After offsetting 740 at least one of the first and second modules withinthe multiplexing signature sequence, the offset module may transmit 750and index number to a corresponding receiving unit. In this regard, thetransmitting 750 of the index number to the corresponding receiving unitmay allow the corresponding receiving unit to similarly advance in themultiplexing signature sequence such that the receiving unitcorresponding to offset module is in sync with the offset module. Inthis regard, the process 700 may include modifying 716 the receivingunit to operate at the same multiplexing signature sequence as theoffset module.

In this regard, the process 700 may include retransmitting 770 datasubject to the data collision with the first and second modules beingout of phase within the multiplexing signature sequence. The process 700may include continuing to transmit 780 data from the first and secondmodule when the first and second modules are out of phase with respectto the multiplexing signature sequence.

An alternative embodiment of a process 800 from deploying a dynamicmultiplexing technique as shown in FIG. 8. The process 800 may includemanually offsetting a first and second module in an identified collisiondomain to be out of phase prior to the occurrence of a new transmission.In this regard, the process 800 may occur at the start up or thedeployment of the units such that there is no data transmission prior tothe modules being manually set to be out of phase. In this regard, theprocess 800 may include assigning 810 a multiplexing signature sequenceto the first and second module. The process 800 may further includeoffsetting 820 at least one of the first and second modules within themultiplexing signature sequence such that the first and second modulesare out of phase from one another with respect to the multiplexingsignature sequence. Again, the offsetting 820 of the modules may bemanually achieved based at least partially on identified collisiondomains within the array.

The process 800 may further include transmitting 830 and indexing numberfrom a respective one of the first and second modules to correspondingreceiving units. The transmitting 830 of an indexing number may allowthe transmitting and receiving unit to become synchronized such thatcorresponding receiving units are in synch with the first and secondmodule with respect to the multiplexing signature sequence. The method800 may further include transmitting 840 seismic data from the firstmodule and the second module using a multiplexing signature sequencesuch that the first module and the second module are out of phase withrespect to the shared multiplexing signature sequence. The process 800may continue transmitting 850 from the first and second module such thatthe first and second modules remain out of phase and the occurrence ofdata collisions is reduced.

Based on the foregoing, it will be understood that for a given number ofmodules in a collision domain, there may be at least a correspondingnumber of unique multiplexing signatures such that each of the modulesmay in turn occupy a point in the sequence out of phase from the othermodules. Based on this, the design of the survey may be modified suchthat on appropriate number of multiplexing signatures may be madeavailable based on the number of modules in a given collision domain.

While described herein as using frequencies, the same principle may alsobe applied wherein the multiplexing signature sequence includesdifferent codes applied to the data and transmitted using code divisionmultiplexing. In this regard, the sequence may be pseudorandom mayinclude a random code generator.

In addition, the wireless modules described herein may be locationaware. In this regard, and as described in U.S. Pat. No. 7,773,457, themodules may have components that are operative to obtain location datafor the module. A module which has obtained location data may transmitits location data to another module in the array which has yet to locateitself. In this regard, the location data transmitted from the locationaware module to the locating module may be used by the locating moduleto acquire a location. For instance, when a GPS module is provided toobtain location data, ephemeris data of a wireless module which is usedto acquire a GPS location may be provided to another module which is yetto acquire a location data from a satellite. In this regard, theephemeris data may be used by the locating wireless module to obtainlocation data. This may improve the locating modules ability to requiresatellite location data. For instance, the time required to acquire asatellite fix may be reduced such that the modules may be deployed andlocated faster.

Additionally, while the invention has been illustrated and described indetail in the drawings and foregoing description, such illustration anddescription is to be considered as exemplary and not restrictive incharacter. For example, certain embodiments described hereinabove may becombinable with other described embodiments and/or arranged in otherways (e.g., process elements may be performed in other sequences).Accordingly, it should be understood that only the preferred embodimentand variants thereof have been shown and described and that all changesand modifications that come within the spirit of the invention aredesired to be protected.

What is claimed is:
 1. A system for use in seismic data acquisition,comprising: a plurality of seismic data acquisition modules, disposed inseries, operable to wirelessly communicate acquired seismic data,wherein said acquisition modules define a wireless serial data transferpath for relaying data from upstream acquisition modules to downstreamacquisition modules and a data collection unit; a first acquisitionmodule in said serial data transfer path for transmitting seismic datausing a first multiplexing signature from a first multiplexing signaturesequence during a first transmission period, wherein said firstacquisition module advances through said first multiplexing signaturesequence in successive transmission periods; and a second acquisitionmodule in said serial data transfer path for transmitting seismic datausing a second multiplexing signature from a second multiplexingsignature sequence during the first transmission period, wherein saidsecond acquisition module advances through said second multiplexingsignature sequence in successive transmission periods; wherein saidfirst acquisition module and said second acquisition module arespatially distributed with respect to said wireless serial data transferpath, and wherein said first acquisition module and said secondacquisition module are synchronized such that said first acquisitionmodule advances within said multiplexing signature sequence atsubstantially the same time as said second acquisition module advanceswithin said second multiplexing signature sequence; and wherein saidfirst multiplexing signature and said second multiplexing signature aredifferent during the first transmission period.
 2. The system accordingto claim 1, wherein said first multiplexing signature sequence and saidsecond multiplexing signature sequence are a common pseudo-randomsequence of a plurality of frequencies.
 3. The system according to claim2, wherein said first acquisition module and said second acquisitionmodule are out of phase with respect to the common pseudo-randomsequence.
 4. The system according to claim 3, further comprising: athird acquisition module in said serial data transfer path fortransmitting seismic data using the first multiplexing signature fromthe first multiplexing signature sequence during the first transmissionperiod, wherein said third acquisition module advances through saidfirst multiplexing signature sequence in successive transmissionperiods; wherein the first acquisition module and third acquisitionmodule are at a first location and a second location, the first locationand second location being separated by a distance greater than thetransmission range of the first and third acquisition module.
 5. Thesystem according to claim 4, wherein the first and third module are inphase with respect to the common pseudo-random sequence.